This invention relates to a shaft of a gas-turbine engine, in particular a radial shaft or a shaft arranged at an angle to the machine axis.
Radial shafts for gas-turbine engines are mostly made of metal. They are used to start the engine, where an electric motor or an air turbine installed in an external gearbox drives the radial shaft via a gear unit. This shaft is connected via a gear unit to the high-pressure compressor of the gas turbine. For starting, the high-pressure compressor is thus put into rotation in order to start the combustion process.
During operation of the engine, the shaft is driven via the same connection in the reverse direction, in order to drive pumps and generators using an external gear unit.
Shafts of this type are subject to the following requirements: firstly the shaft has to be constructed very slender, since it must be passed through a strut in the intermediate casing or as a general principle through the second air circuit in the case of a dual-circuit/dual-flow turbine jet engine, and hence always represents a fluid-mechanical resistance which directly affects engine output and efficiency. With regard to its geometric configuration, the shaft must be passed through openings in the engine suspension in order to connect the external gear unit to the high-pressure compressor. A further requirement is that the shaft must transmit high torques at high speeds in both directions.
Radial shafts made of metal, as known from the state of the art, come up against the limits of their usability for engine design, as these shafts are already designed to the limit of the bending-critical speed. The materials used do therefore not permit any lengthening or slimming down of the shaft geometry, which considerably hampers the development of gas-turbine engines having a smaller core engine with higher speeds and a larger fan diameter. With a larger fan and a smaller diameter of the core engine, the result is a greater distance between the core engine and an external gear unit (gearbox), which would inevitably result in longer radial shafts. They would, in the metal construction method known from the state of the art, have to be designed with thicker walls, be of larger size and, due to the problem of bending, have a centric bearing as a support. This would lead to a higher weight of the overall engine plus poorer aerodynamics.
Already known from the state of the art are engine shafts for gas-turbine engines, which are constructed from fiber layers embedded in a high-temperature resistant plastic matrix. An example of this type is shown by DE 10 2008 056 018 A1. Such shafts have a large diameter and can have other dimensions, so that the application of this knowledge to radial shafts is not possible. Furthermore, in these engine shafts power transmission elements are in use which have a design unsuitable for radial shafts. Examples of this are shown by DE 10 2009 037 049 A1, GB 1 599 292 A and DE 41 07 222 C2.